1. Field of the Invention
The present invention relates to a broadcast/communication convergence system. More particularly, the present invention relates to broadcasting in an FTTH (Fiber To The Home) system.
2. Description of the Related Art
Current communication/broadcast subscribers have the choice of employing a data service chosen from a plurality of data services, such as a very high-speed Internet service, etc. via an ADSL (Asymmetric Digital Subscriber Line), VDSL (Very High Bit-Rate Digital Subscriber Line), Ethernet LAN (Local Area Network), cable modem, etc., and may also employ broadcast services from at least one of cable and satellite broadcasting based on an HFC (Hybrid Fiber Coaxial) system. In other words, the subscribers have the option to employ different mediums to receive the communication and broadcast services. In cases where there are a combination of protocols, a communication service rate is only several Mbps.
In order that high-speed, large-capacity communication/broadcast services can be provided to the subscribers to overcome limitations of older protocols, an FTTH (Fiber To The Home) system for coupling an optical fiber to the subscriber's premises or home is considered to be the best solution. FTTH systems that provide high-speed, large-capacity communication/broadcast services can be classified into one of a PON (Passive Optical Network) and an AON (Active Optical Network).
In order for broadcast/communication convergence to be performed using the FTTH system, there has been proposed an FTTH system for broadcast/communication convergence as shown in FIG. 1. The FTTH system for broadcast/communication convergence shown in FIG. 1 comprises an OLT (Optical Line Terminal) 300, an ONU (Optical Network Unit) 400 and a gateway 500. The components for broadcast/communication convergence perform the following operations.
First, the OLT 300 receives digital broadcast information 100 and external data communication (VOD (Video On Demand), Internet or etc.) information 200 via an external broadcasting network, electro-optically converges received signals into an optical signal, and transmits the optical signal using optical WDM (Wavelength Division Multiplexing) via a WDM 106.
Moreover, the ONU 400 demultiplexes the WDM optical signal received from the OLT 300 into broadcast and communication signals via WDM 107, opto-electrically converts the broadcast and communication signals, processes upstream information received from a subscriber, and carries out a TDM (Time Division Multiplexing) operation for the broadcast and communication signals selected user by user, and transmits a TDM signal.
The gateway 500 carries out a TDDM (Time Division Demultiplexing) operation for the TDM signal received from the ONU 400 and distributes a result of the TDDM operation service by service. The gateway 500 optically transmits the upstream information from the subscriber to the ONU 400.
Now, the components will be described in detail. The OLT 300 shown in FIG. 1 includes: a broadcast MUX (Multiplexer) 101 for receiving digital broadcast signals and multiplexing the received digital broadcast signals; an optical transmitter 102 for converting the multiplexed broadcast signals into an optical signal; a communication switch 103 for receiving the Internet/VOD information 200 to carry out a downstream switching operation for the received Internet/VOD information 200 and receiving an upstream communication signal from each subscriber to carry out an upstream switching operation for the received upstream communication signal to a network for the Internet/VOD information 200; an optical transmitter (Tx) 104 for converting a downstream communication signal into an optical signal; an optical receiver (Rx) 105 for receiving an upstream optical signal and converting the received upstream optical signal into an electrical signal; and a wavelength division multiplexer 106 for carrying out a WDM (Wavelength Division Multiplexing) operation and transmitting a result of the WDM operation.
Moreover, the ONU 400 shown in FIG. 1 includes: a wavelength division demultiplexer 107 for separating an optical signal received from the OLT 300 into broadcast and communication signals; a broadcast DEMUX (Demultiplexer) 108 for separating the broadcast signals received from the wavelength division demultiplexer 107 on a broadcast channel-by-channel basis; a broadcast switch 109 for switching the broadcast signals separated channel by channel according to the subscriber's selection operation; a communication switch 112 for switching a downstream communication signal separated from the wavelength division demultiplexer 107 subscriber by subscriber and switching an upstream communication signal received from the subscriber to the OLT 300; time division multiplexers 110-1 to 110-n for carrying out a TDM operation for the broadcast and communication signals subscriber by subscriber; and optical transceiver (Tx/Rx) 111-1 to 111-n for transmitting the broadcast and communication signals multiplexed by the time division multiplexers 110-1 to 110-n to respective subscribers (or gateways) and transmitting upstream signals from the subscribers to the communication switch 112 via the time division multiplexers 110-1 to 110-n.
Moreover, each gateway 500, as shown in the exploded view in FIG. 1, includes: a transceiver (Tx/Rx) 113 for receiving a downstream signal from the ONU 400 and transmitting an upstream signal to the ONU 400; a time division demultiplexer 114 for separating the broadcast and communication signals multiplexed by the TDM operation; and a communication switch 115 for receiving the communication signal from the time division demultiplexer 114 to transmit the received communication signal to a communication unit such as an Internet/PC (Personal Computer) 118 of the subscriber, etc., and receiving an upstream signal from the communication unit (such as the Internet/PC 118, etc.) to transmit the received upstream signal to the ONU 400.
After receiving the broadcast signals transferred from the time division demultiplexer 114, the subscriber decodes the broadcast signals through an STB (Set-Top Box) 116, views the broadcast on a digital TV (Television) 117, and can access the network by transmitting and receiving the communication signals sent through the Internet/PC 118.
The conventional FTTH system for broadcast/communication convergence carries out a TDM operation for the broadcast and communication signals to transmit a result of the TDM operation according to a connection between the ONU 400 and the gateway 500, and subsequently carries out a TDDM operation. However, the conventional FTTH system has problems when accommodating items such as a multi-channel broadcast signal or a broadband communication signal.
The reason that the conventional FTTH system for broadcast/communication convergence has problems accommodating multi-channel broadcast signals or broadband communication signals is that the FTTH system employs a TDM operation for multiplexing a communication signal (e.g., Ethernet data) between the ONU 400 and the gateway 500 at a subscriber side and broadcast signals selected by the subscriber into one time frame, followed by transmitting a result of the multiplexing. Here, the time frame is generated through an FPGA (Field Programmable Gate Array). In this case, the FPGA can accommodate only a 100-Mbps Ethernet signal and a maximum of two HD (High Definition) channels because of the limitations of its processing rate. In particular, the FPGA is designed so that it can accommodate only fixed-length broadcast signals. For this reason, the conventional FTTH system for broadcast/communication convergence is not capable of accommodating broadcast signals based on various standards (e.g., broadcast signals of various wavelengths), and cannot accommodate three-channel broadcast signals.